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SW180 little tweak of the collimation

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#1 Stopforths

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Posted 15 April 2019 - 01:34 PM

Just had a season on jupiter in what looked like good seeing but images weren't what i would expect of the sw180.

 

defocused a star and saw why collimation out a little bit.  I've added a focuser to the rear and was using a tak prism maybe this is why??

 

Anyway I used a simple system to id the  adjustment needed ( an object I could see over the front lined up with collimation screws.)

 

Then went to a star near the southern pole defocused and made a little adjustment which made it worse.  reversed this a couple of times checking and centering star each time and pretty much found perfection.  i was using 233 x a 12.5mm ortho.

 

Then went to jupiter and oh boy what an improvement ovals festoons grs coming round  amazing detail.  its virtually overhead here at 0500 in the morning.

 

I left scope out to acclimatize overnight. 

 

Collimation is so important and relatively easy with a sw mak.


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#2 Cali

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Posted 15 April 2019 - 01:37 PM

What focuser did you add?

 

- Cal



#3 macdonjh

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Posted 15 April 2019 - 01:52 PM

 

Collimation is so important and relatively easy with a sw mak.

Agreed, collimation is likely the most important variable that an observer can control in determining how good an image his scope will produce.  Seeing might be more important, but who can control seeing?



#4 Stopforths

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Posted 16 April 2019 - 11:22 AM

a gso crayford 10/1

 

works great.  there is a little mirror shift in the sw180 and the sw focuser isn't precise enough for my liking also its a bit stiff.

 

I also have a IM10 inch mak cass and the focuser on that is next to useless even after a reassembly.  I use a gso on that also and it works great.

 

Its a slow difficult process using that scope without the gso and I'm glad I have one.  Shame because optics are superb in the big Mak.

 

Just got in after a season on jupiter in the 10  seeing came and went but at 280 x there was plenty to see.

 

 

 

What focuser did you add?

 

- Cal



#5 Bill Barlow

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Posted 17 April 2019 - 09:26 AM

When you adjusted the collimation on your 180 MAK, did you loosen the one large mirror lock screw and adjust the smaller collimation screw where the adjustment was needed?  Or did you loosen all three large primary mirror locking screws and then adjust the smaller one?  Also, what is the diameter of the rear cell opening in these scopes?  Thanks.

 

Bill



#6 Peter Besenbruch

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Posted 17 April 2019 - 09:48 PM

When I collimated my 180, I loosened the three small screws, collimated with the three big screws, and very gradually tightened the three little screws. Of course, it helps if the scope is pointing up, you use very high powers, and you keep re-centering the star. Also, it's a good idea to collimate straight through if you are at all uncertain about your diagonal's alignment.



#7 luxo II

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Posted 18 April 2019 - 06:06 AM

Collimation is important - PERIOD.

Many users think “near enough is good enough” without realising that the difference between nailing it spot on vs “a bit off” is cheese vs chalk.

Laser collimation gadgets will get it close but not perfect - there is no substitute for collimating on a real star.

And this applies to all cassegrains, maks and SCTs - as well as newtonians and refractors.

For a SW mak, follow Peters advice above. The target star should be 70 degrees elevation or higher.

Edited by luxo II, 18 April 2019 - 06:17 AM.


#8 Bill Barlow

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Posted 18 April 2019 - 09:13 AM

When I collimated my 180, I loosened the three small screws, collimated with the three big screws, and very gradually tightened the three little screws. Of course, it helps if the scope is pointing up, you use very high powers, and you keep re-centering the star. Also, it's a good idea to collimate straight through if you are at all uncertain about your diagonal's alignment.

Someone on another thread that owns a SW 180 MAK said he collimated using the three smaller screws and tightens down the primary mirror with the large ones.  I guess you can collimated both ways then?

 

Bill



#9 fcathell

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Posted 18 April 2019 - 02:27 PM

Peter B. made a good point about having the scope pointing up rather than being horizontal as it probably would be with an artificial star. Due to the mirror's downward weight, I can see how loosening all of the similar collimation screws would be advantageous.  With a horizontally mounted scope this would not be recommended due to the mirror's weight pushing laterally.  In this case tiny incremental adjustments must be made with subsequent snugging of individual screw sets each time.

 

Frank



#10 Peter Besenbruch

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Posted 18 April 2019 - 02:43 PM

Someone on another thread that owns a SW 180 MAK said he collimated using the three smaller screws and tightens down the primary mirror with the large ones.  I guess you can collimated both ways then?

My understanding is that the little screws function as lock screws and the big screws do the actual pushing around. What I like about the 180 is that they are paired.



#11 Peter Besenbruch

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Posted 18 April 2019 - 02:44 PM

Peter B. made a good point about having the scope pointing up rather than being horizontal as it probably would be with an artificial star. Due to the mirror's downward weight, I can see how loosening all of the similar collimation screws would be advantageous.  With a horizontally mounted scope this would not be recommended due to the mirror's weight pushing laterally.  In this case tiny incremental adjustments must be made with subsequent snugging of individual screw sets each time.

Agreed.



#12 James Ball

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Posted 18 April 2019 - 06:32 PM

I have the SW150 and need to check the collimation, just wondering if 180x is enough magnification or if I need to pick up a higher magnification eyepiece.  Right now I only have a 25mm Meade that came with the ETX90 and the 10mm VixenLV.



#13 Peter Besenbruch

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Posted 19 April 2019 - 08:43 PM

I have the SW150 and need to check the collimation, just wondering if 180x is enough magnification or if I need to pick up a higher magnification eyepiece.  Right now I only have a 25mm Meade that came with the ETX90 and the 10mm VixenLV.

The 10mm should be adequate, especially if you don't defocus the star too much.



#14 luxo II

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Posted 20 April 2019 - 02:54 AM

10mm is more than short enough - it gives 270X.

#15 Peter Besenbruch

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Posted 21 April 2019 - 12:58 AM

10mm is more than short enough - it gives 270X.

And when you finish collimating, Jupiter begins to shine at that magnification.



#16 Rock22

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Posted 22 April 2019 - 01:38 AM

I tried collimating using the instructions in the manual for the Orion 180mm mak. Almost like collimating a Newtonian. Didn’t work.

Then I spent most of tonight trying to collimate using a defocused bright star, but couldn’t figure out how to adjust the screws to get the circular pattern. The rings were still squished at the bottom right.

I’ll be trying Peter’s method tomorrow night.

Edited by Rock22, 22 April 2019 - 01:48 AM.


#17 Paradoxdb3

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Posted 22 April 2019 - 05:59 AM

I am just about done trying to collimate mine. Quite frustrated at the moment.

At first, I used a long hallway (about 200 feet) and put an artificial star at one end, with my scope at the other. Because it was a controlled environment, and it was cloudy out, this was my best option. And I got it spot on after some trial and error. But when I went out the next night to test on a real star, my collimation was quite off. I've been struggling with it for a couple of days now, and STILL don't have spot on collimation. When it looks like my collimation is good on the inward defocus, it is off on the outward defocus. I honestly can't figure out what's going on.

I am using my camera as the eyepiece, and keeping the target star centered in the frame. I make small adjustments of only one set of screws at a time. I loosen the small screw by a quarter or half a turn, and then tighten the larger one by about the same. If I've gone the wrong way, then I loosen the larger, tighten the smaller to return where I was, and then loosen the larger again, and tighten the smaller again to move the mirror in the other direction. Seems to work. Then I adjust the other sets of screws in the same way, if needed.

It's been two frustrating nights of nothing gone right. I have a Celestron C5 as well, and it was such an easy task to get it BANG ON PERFECT collimation. This SkyWatcher, though? What gives?

#18 nirvanix

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Posted 24 April 2019 - 11:22 AM

Hey Paradox, your situation sounds similar to what I went through a month ago with my Vixen VMC. It's best to use a real star of moderate brightness and elevation over 45 degrees. I would concentrate on the in-focus star pattern. Try to get a nice airy disc and a first diffraction ring evenly illuminated all the way around.

 

Don't forget after getting collimation the screws have to be snugged. It sounds like yours is a push-pull arrangement? If so, you can't leave any play between each pair, if you understand my meaning.

 

As to why you're seeing two different patterns inside and outside focus - might be caused by something tilted slightly to the optical axis (diagonal, camera, secondary, etc). I had the same problem, and I had several tilt issues which I sorted out. You'll get it sorted eventually.

 

This winter/spring I've spent a good amount of time working on collimation on all my scopes, taking them from 98% to as perfect as I could make them. It makes a difference for doubles splits and fine lunar/planetary detail.


Edited by nirvanix, 24 April 2019 - 11:23 AM.


#19 Rock22

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Posted 24 April 2019 - 12:34 PM

I agree with Nirvanix.  I collimated my 180mm mak (Orion version) two nights ago using Polaris.  It took me quite a while to figure out the push-pull procedure (I'm a pretty patient guy), but I now have good collimation.  Not great yet, but very good.  I'll tweak it some more when I have a chance.

 

Once I figured out whether to loosen the big or small screw to get the circles to move in the direction I needed, it was much easier.  You want to move the image in the direction of the thinner lines, as this will make them thicker.  You can also see it as moving the darker middle circular area toward the center, thus 'unsquishing' that squished area.  If the rings are squished toward the bottom right, for example, you can see it as the middle of the circle needing to be moved toward the upper left.

 

1. I used an 11mm 82-deg EP straight through to Polaris (no diagonal).

 

2. Defocused to see the rings clearly and where they were "squished".  If I didn't see the rings clearly, I defocused the other way.

 

3. The rings were squished at the bottom right of what I saw, so I used the push-pull screws that were toward the bottom right of the rear of the scope (relative to how I had the scope mounted).

 

4. I loosened either the 4mm or 2.5mm screw and saw if it moved the squished lines toward the edge of the field of view.  If not, I retightened and loosened the other one.

 

5. After I loosened one and the star moved, I recentered the star.  I kept doing this until the rings were not squished on that side.  I kept recentering the star after every turn of the screw.

 

6. When the circles were no longer squished on that side, I tightened the other screw (of the push-pull pair) lightly until the mirror position was secure, recentering the star as needed.

 

7. I repeated in the other directions with the other push-pull screws.

 

8. When done and the rings were concentric, I defocused in the other direction to see if the circle was symmetrical.  One part was thicker than the other, so I collimated it the same way.

 

The problem I had with Polaris is that there is a companion star that made it seem there was flaring in one direction.  I will use another star when I have a chance.

 

One other thing I noticed that helped me was that while collimating, I saw that one part of the circled seemed a little brighter than the opposite part even though the circles were concentric. I found that the circle needs to be consistently the same brightness all around to be collimated well.  In other words, just getting the rings symmetrical is not enough.  The brightness must also be symmetrical.  I played around with the push-pull to get the brightness consistent.

 

Hope this helps.



#20 Paradoxdb3

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Posted 24 April 2019 - 05:33 PM

Thank you for the replies. I am not sure if I should proceed further, but what I ended up doing was (using my camera) moving the star to the part of the frame that looked like it had the best collimation, and then adjusting the screws until the star was centered. Seemed to work. These are my results. When defocused close to focus, the Poisson spot looks pretty good. When I defocus far out both directions, there is a minor discrepancy, albeit very small. I'm not sure it's worth me playing around with it any more. Please feel free to critique. And thanks again for the replies. I quite appreciate it!

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#21 Nakedgun

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Posted 24 April 2019 - 09:58 PM

The two bottom images show you're off just a bit, yet.



#22 Paradoxdb3

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Posted 25 April 2019 - 08:28 PM

Yeah, I know, but I am not sure how much I am willing to fiddle around. And as it was told to me before, the closer focus is the best indicator. We'll see how brave I get tonight! Lol.

#23 doug mc

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Posted 25 April 2019 - 08:48 PM

Fiddle only in very small adjustments. Cassegrains are very sensitive.



#24 Paradoxdb3

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Posted 25 April 2019 - 09:18 PM

I hear ya! I've gone this way and that, only to have to do it all over again. I really don't want to spend an hour collimating, which is why I may leave it the way it is. It's not perfect, but as someone once said, perfect is the enemy of good! Haha.

#25 luxo II

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Posted 26 April 2019 - 07:01 AM

Sounds like after adjustment the push-pull screw pairs are loose, they need to be done up only to take out the slack ie so there is no movement - not tight.

I’ve had three SW180 maks and once colliminated properly they stayed that way for years, just be gentle with it and don’t knock the tube around.

Edited by luxo II, 26 April 2019 - 07:04 AM.



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